The existing electrophoretic buffer is excellent in separation ability to a limited size. However, since a polymer having a high viscosity (methylcellulose, hydroxylcellulose, polyacrylamide or the like) is used as a buffer, there are some defects 1) that it takes time to inject the buffer into a microchannel, 2) that the injection becomes more difficult, as a channel width becomes narrower, 3) that it is necessary to change a polymer concentration depending on a size of a DNA, and there is a limitation of a separation degree to separation of a wide range of a DNA size, 4) that viscosity of the buffer is sensitive to temperature, and the like. Therefore, there is desired an electrophoretic buffer which does not have the problems of the above-mentioned 1) to 4) and is capable of separating a polymer compound rapidly and at high separation ability. In addition, there is desired an electrophoresis method which is capable of separating a polymer compound rapidly and at high separation ability.